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United States Department of Agriculture

Agricultural Research Service

Research Project: BIOLOGICAL CONTROL OF INVASIVE PLANTS OF THE NORTHERN GREAT PLAINS

Location: Pest Management Research Unit

Title: Latitudinal variation in cold hardiness in introduced Tamarix and native Populus

Authors
item Friedman, J - USGS
item Rolle, J - USGS
item Gaskin, John
item Pepper, A - TEXAS A&M
item Manhart, J - TEXAS A&M

Submitted to: Ecological Applications
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 15, 2008
Publication Date: August 21, 2008
Repository URL: http://hdl.handle.net/10113/44927
Citation: Friedman, J., Rolle, J., Gaskin, J.F., Pepper, A., Manhart, J. 2008. Latitudinal variation in cold hardiness in introduced Tamarix and native Populus. Evolutionary Applications. 1(4):598-607.

Interpretive Summary: Native woody plants often demonstrate inherited latitudinal variation in cold hardiness. How long does it take for such variation to evolve in introduced species? We compared cold hardiness in the native plains cottonwood and the introduced saltcedar. We found that frost sensitivity, appears to be a factor limiting northward expansion of saltcedar in North America. There is strong inherited latitudinal variation in cold hardiness for both species. Hybridization between these two saltcedar species may have introduced the genetic variability necessary for rapid evolution of the latitudinal gradient in cold hardiness.

Technical Abstract: Native woody plants often demonstrate inherited latitudinal variation in cold hardiness. How long does it take for such variation to evolve in introduced species? We compared cold hardiness in the native plains cottonwood (Populus deltoides subsp. monilifera) and the introduced saltcedar (Tamarix ramosissima, T. chinensis and hybrids). In February and March 2005, we collected cuttings of 25 individuals of each species from 15 sites in the central U.S. ranging in latitude from 29ºN to 48ºN. Cuttings were rooted in a greenhouse and then moved to a shadehouse in Fort Collins, CO, latitude 41ºN, on May 31. Seventeen times between September 2005 and June 2006, we exposed stem sections of northern and southern individuals of both species to a range of cold temperatures and determined the killing temperature using freeze-induced electrolyte leakage and direct observation. Although saltcedar was slightly more cold hardy in the early fall and late spring, cottonwood hardened off more rapidly and deeply. In midwinter, cottonwood was unharmed by cooling to -70'C, while saltcedar was killed at -30 to -40'C, which is within the temperature range of the northern Great Plains. Frost sensitivity, therefore, appears to be a factor limiting northward expansion of saltcedar in North America. There is strong inherited latitudinal variation in cold hardiness for both species. Plants from the north survive colder temperatures earlier in the season than plants from the south. Analysis of 9 microsatellite DNA loci shows a north-south genetic gradient in saltcedar in the central U.S.; southern saltcedar is more closely related to T. chinensis and northern saltcedar is more closely related to T. ramosissima. Hybridization between these two Tamarix species may have introduced the genetic variability necessary for rapid evolution of the latitudinal gradient in cold hardiness.

Last Modified: 8/22/2014
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